mac80211: use synchronize_net() on key destroying

__ieee80211_key_destroy() calls synchronize_rcu() in
order to sync the tx path before destroying the key.

However, synching the tx path can be done with
synchronize_net() as well, which is usually faster
(the timing might be important for roaming scenarios).
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/key.c

@@ -402,7 +402,7 @@ static void __ieee80211_key_destroy(struct ieee80211_key *key)
 	 * Synchronize so the TX path can no longer be using
 	 * this key before we free/remove it.
 	 */
-	synchronize_rcu();
+	synchronize_net();
 
 	if (key->local)
 		ieee80211_key_disable_hw_accel(key);